1. Field of Use
This invention relates to apparatus and methods using a portable pump to mix, remove and dispose of fluid material, such as sewage, accumulated in a tank, such as a septic tank, storage pond or the like.
2. Description of the Prior Art
In some industrial processes or in various kinds of systems, such as sewerage systems, it is necessary to accumulate fluid or liquid material in one tank or container and to periodically pump it into another tank for further processing or disposal. The type of process, the nature and composition of the fluid or liquid material, and the location and purpose of the tanks dictate the apparatus and methods to be employed. In some cases the fluid or liquid material takes the form of a mixture of liquids of different specific gravities or a mixture of liquid and solid particulate matter. However, the liquids may separate or the solid particulate matter may settle out and it is sometimes necessary to remix the material before pumping it from one tank to the other. In the case of sewage comprising a mixture of liquid and solid particulate matter, including organic waste material, dirt and sand, special problems can arise.
For example, large municipal sewerage systems typically employ an "aerobic" digestive treatment process wherein liquid waste material and solid waste material is constantly stirred and mixed in a tank by mechanical means while the biochemical treatment is occurring, and, therefore, such an emulsified, fluidized effluent can easily and efficiently be pumped from one tank to another.
However, smaller sewerage systems typically employ a septic tank or holding pond to receive and accumulate sewage supplied from residential and commercial buildings. These septic systems employ an "aerobic" digestive treatment process wherein the sewage in the septic tank or holding pond is not stirred while the biochemical treatment is occurring. The sewage typically comprises a fluid mixture of liquid waste material, solid organic waste material, and solid inorganic waste material, such as sand or dirt. The unstirred sewage in the septic tank or pond gradually undergoes chemical, biochemical and physical changes with the following results: a relatively heavy sludge of mud-like consistency, including solid particulate waste material and sand, settles out at the bottom of the septic tank or holding pond; clarified and relatively clean water accumulates in a digestive zone above the sludge; and relatively light solid waste material floats to the surface of the water and gradually dries to form a crust of earth-like consistency. Most of the clarified liquid is eventually drained off by gravity to a drainage field connected to the septic tank or holding pond. However, over a period of time sludge and crust build up in the septic tank or holding pond must be periodically removed and disposed of so as to restore the tank or pond to its full processing capacity. In a storage pond, the layers of sludge and crust can each reach several feet in thickness. In a septic tank, each layer may be on the order of 11/2" to 18" in thickness.
Two types of septic tanks are in general use. One is a concrete box (on the order of 5 feet deep, 4 feet wide and 7 feet long) buried in the earth and having its open top side (flush with ground level) closed by a lid or cover in the form of removable concrete slabs. The other is a cylindrical tank (typically fiberglass or plastic) disposed horizontally underground and having relatively small access openings (about 11/2" in diameter) at opposite ends (flush with ground level) which are closed by removable hatch covers or plates.
Periodic cleaning of such septic tanks involves break-up of the crust; removal of the broken crust, sludge and water remaining in the septic tank; and transport thereof to and unloading at a suitable disposal site. Prior art apparatus for this purpose typically comprises a vehicle, such as a truck or trailer driven or towed to the jobsite, having the following equipment mounted thereon, namely: a sewage holding tank, a pump permanently mounted on the vehicle, a prime mover for driving the pump (such as a PTO on a truck engine or a separate internal combustion engine mounted on a trailer); necessary hose-sections and valving, all connectable for operation by the equipment operator at the jobsite; and suitable hoe-like or paddle-like tools to manually break up the crust and to mix the waste materials in the septic tank to provide a fluidized mixture which the pump can handle.
Prior art techniques employed by the operator to effect manual crust break-up and mixing by means of tools involve difficult, time-consuming, costly and dirty manual labor. Often, fresh water is introduced into the septic tank through a garden hose to dilute the mixture and facilitate pumping. Of course, addition of fresh water increases the volume of sewage to be pumped from the septic tank, requires a vehicle-mounted holding tank of larger capacity than would otherwise be needed, and increases the disposal fees at the disposal site, which are charged for on a volume basis. In addition, since the size and location of the hatch openings in a cylindrical-type septic tank limit access to the tank interior, prior art techniques involving insertion and manipulation of hand tools are not well-suited to permit thorough crust break-up and mixing, and some operators limit themselves to removing only liquids remaining in the septic tank and ignore the unbroken crust and sludge.
Furthermore, the types of pumps and hose arrangements used in prior art septic tank cleaning systems and apparatus are not efficient. Typically, such pumps are permanently mounted on the vehicle and the intake side of a pump is connected to the septic tank by large-diameter (3" or more) hose sections carried on the vehicle and manually assembled and connected at the jobsite. Unless such hose sections are thoroughly flushed out by clean water after use and prior to restorage on the vehicle, sewage remaining in the hose sections dries out and cakes therein, thereby reducing effective hose diameter for subsequent use and serving as a source of foul and offensive odors.
As to the pumps used in prior art systems, the oldest, least-productive and now least-used type is a diaphragm pump which "sucks" the effluent from the septic tank. This pump, which employs a mechanically driven flexible diaphragm to draw a vacuum on one side, employs two ball-type check valves, one each at the inlet and outlet ends of the pump, has several drawbacks. For example, an appropriately-sized pump of this type is inefficient and exerts only a limited net positive suction head (typically 10.8 psi). In addition, pump volume drops off from 5280 gallons per hour at a 5-foot head to 3500 gallons per hour at a 25-foot head, for example. Furthermore, pump stroke or action is pulsating, intermittent and jerky and debris and sludge tend to hang up in the check valves which then need to be disassembled and cleaned while the system is shut down.
Another prior art system is similar to that above-described but uses a truck-mounted self-priming trash pump, such as a "midwhirled" or "impressed vortex" type trash pump, instead of a diaphragm pump. However, although this type of pump requires only one check valve for priming and this valve is not easily clogged, this type of pump is only slightly more efficient than the diaphragm pump (dropping as low as 20% to 10% efficiency when it becomes unprimed) and imposes a time-delay while it is being reprimed.
Still another prior art system, which is presently most widely used, employs a vehicle-mounted vacuum pump which is connected to a holding tank mounted on the vehicle. The tank must be of heavy-duty construction because it is subjected to high internal vacuum (20 to 25 inches of mercury) when the vacuum pump operates to "suck" effluent thereinto from the septic tank and is subsequently subjected to high internal pressure (i.e., up to 14 psi) when the vacuum pump is operated in reverse to expel effluent from the holding tank for ultimate disposal. The vacuum pump is provided with inlet and outlet valves aimed at preventing effluent from entering thereinto. The drawbacks of this system are that the valves are trouble-prone and can be clogged, the vehicle-mounted holding tank must be relatively strong and heavy to withstand both high vacuum and high pressure, and large diameter (about 3" diameter, for example), multi-section connectable/disconnectable cam-lock type hoses must be stored on the vehicle, assembled and disassembled, and internally cleaned.
Using a pump which is permanently mounted on the vehicle to empty a septic tank which is typically located at a relatively long distance from the pump substantially reduces pump and system efficiency. Insofar as applicant is presently aware, no prior art system uses a portable pump, powered from a power supply source on the vehicle, which can be removed from the vehicle and disposed near or in the septic tank to effect pumping of effluent therefrom into a holding tank on the vehicle or to effect mixing and subsequent pumping. Furthermore, applicant is unaware of the use of such a portable pump, when stored on the vehicle, to recirculate effluent in the vehicle-mounted holding tank and to discharge it therefrom.
U.S. Pat. Nos. 3,910,728, 4,352,251 and 4,529,359, all owned by the same assignee as the present application, disclose portable submersible pumps and means for driving such pumps. However, none of these patents disclose the use of a portable pump, such as a submersible pump, to remove effluent from a septic tank or holding pond and deliver it to a holding tank. Furthermore, none of these patents disclose use of a portable pump, such as a submersible pump, to mix liquid in one vessel, such as a septic tank, and to subsequently transfer the mixed liquid to another vessel, such as a vehicle-mounted holding tank. None of these patents discloses use of a portable pump on a transport vehicle which is usable to clean a septic tank and is further usable to mix and discharge effluent carried in a holding tank thereon.